The purpose of the research is to study the interaction of immunoglobulins with lymphocytes. The binding of unaggregated and aggregated myeloma proteins to different types of lymphocytes will be investigated both in man and rats. ParticPlar emphasis will be placed on the binding of IgE to lymphocytes and the four IgG subclasses to K type lymphocytes. In addition, myeloma proteins having deletions in the third constant domain are also studied for their ability to bind to Fc receptors in order to learn more on the submolecular structures involved in the binding to cell receptors. In a different project, the physicochemical properties of myeloma, serum and cell-bound IgD will be analyzed and compared in order to determine if cell-bound IgD is completely or only partially identifical to serum IgD. BIBLIOGRAPHIC REFERENCES: Lawrence, D.A., W.O. Weigle and H.L. Spiegelberg. 1975. Immunoglobulins cytophilic for human lymphocytes, monocytes and neutrophils. J. Clin. Invest. 55:368. Spiegelberg, H.L., V.C. Heath and J.E. Lang. 1975. IgG half-molecules: Clinical and immunological features in a patient with plasma cell leukemia. Blood 45:305.